1. Field of the Invention
The invention relates to a fluid delivery system, and more particularly to a biological fluid delivery system having a sterile disposable assembly which interfaces with a plurality of sensors which are integrally apart of the fluid delivery system.
2. Background
In the performance of open heart surgery, the patient is supported by an extracorporeal blood circuit employing a heart/lung machine. The heart is isolated from the vascular system, and venous blood is diverted into the extracorporeal blood circuit where it is oxygenated, temperature-controlled, filtered and returned to the patient's arterial side. A separate circuit is established for supplying a cardioplegic solution to the heart as the surgery proceeds.
The cardioplegia circuit functions to still the heart, lower the metabolic requirements of the heart, protect the heart during periods of ischemia, and, finally, prepare the heart for reperfusion at the end of the procedure. Operation of the extracorporeal blood circuit as well as the cardioplegia delivery is performed by a trained perfusionist under the direction of the surgeon. The principal elements of cardioplegia solution are blood, representing a small fraction diverted from the output of the heart/lung machine, combined with a crystalloid solution. A minor but critical amount of potassium solution is added to the cardioplegic flow to still the heart. Still further, other fluid additives may be combined with the cardioplegia fluid as necessary to address particular patient conditions or procedure requirements.
Depending upon the requirements of the particular surgery, the cardioplegia solution may be cooled or warmed, and may be delivered in antegrade fashion to the aortic root, or in a retrograde mode to the coronary sinus. The requirements placed upon the cardioplegic solution vary as the surgery proceeds, and are subject to the clinical judgment of individual surgeons.
A typical cardioplegia delivery system employs two tubes routed through a single rotary peristaltic pump to forward both the separate blood and crystalloid solutions to a Y combining the two into a single flow. The ratio between the blood and crystalloid solution is determined simply by the relative diameters of the tubing carrying the two solutions, since each is mounted on the same rotary peristaltic mechanism and thus is forwarded by the same action. The tubing is usually provided in a 4:1 ratio of blood to crystalloid cross-sectional flow area, so that the rotary peristaltic pump is delivering blood and crystalloid to the delivery line in a ratio of approximately 4:1. Potassium is typically provided to the delivery line upstream of the pump from two alternate crystalloid solutions containing potassium, one having a relatively low concentration of potassium, the other a higher concentration. The perfusionist selects between the two sources to initiate or control an arrested state of a patient's heart. The higher potassium concentration is utilized to arrest the heart, while the lower is used to maintain the stilled condition. The clinical team must provide sufficient potassium in the cardioplegia solution to establish the stilled condition of the heart and maintain it during the procedure, while avoiding the risks associated with hyperkalemia which may result from excessive potassium.
Without regard to the specific protocol or technique employed, cardioplegia fluid delivery requires control of cardioplegia fluid temperature and pressure and the delivery of an air-free solution. Consequently, cardioplegia delivery systems employ pressure and temperature sensors; certain controls to adjust fluid temperature and pressure based on the data provided by said sensors (for example, heat exchangers); and other devices to filter the potentially dangerous air or gas bubbles from the cardioplegia fluid.
Current cardioplegia delivery systems do not provide integral pressure or temperature monitoring. With regard to pressure monitoring, the perfusionist is required to add a pressure sensor, or a pressure gauge, at a selected point within the fluid system, thus necessitating the assembly of additional sterile components which are costly and are subject to being assembled incorrectly. A fluid pressure isolator, a device which separates the sterile cardioplegia fluid from a nonsterile pressure sensor using a protective membrane, is commonly used in known cardioplegia systems. Fluid pressure isolators dampen the measured pressure due to air compliance within said devices. Temperature monitoring requires the addition of a temperature probe, in a conductive sheath, to be inserted into the system heat exchanger.
Cardioplegia delivery system heat exchangers typically use a temperature controlled water source across a thermally conductive medium to influence and adjust the temperature of the cardioplegia fluid. The temperature controlled water is pumped from warm or cold water reservoirs, the reservoirs being coupled to the heat exchanger, directly or indirectly through a holder. In addition to the physical configuration and its related impact on the efficiency of a heat exchanger, a number of system variables influence the device's effectiveness: the cardioplegia solution flow rate, the cardioplegia solution inlet temperature and the flow rate and temperature of the temperature controlled water. As current systems permit only the manual influence of the temperature of the water circulated through the heat exchanger, precise control of the delivery temperature of cardioplegia fluid is severely limited.
Various devices are utilized in an effort to remove potentially harmful gas bubbles from cardioplegia fluids (or other biological fluids) prior to delivery. One such device is a bubble trap. The bubble trap acts to separate, through fluid flow, any trapped gases within the fluid. As bubble traps are enclosed, the separated gas accumulates in the interior of the device. Current bubble trap devices have limited capacity and require manual venting. Consequently, the perfusionist must closely monitor and react when the bubble trap requires venting. An alternative design utilizes a microporous hydrophobic membrane to vent air from the system. Although initially effective, such membranes degrade when exposed to blood proteins vitiating the effectiveness of these devices.
A need is shown to provide an improved biological fluid delivery system which utilizes a sterile disposable component to combine the functions of temperature control, gas separation and/or filtration of a biological fluid. Moreover, the sterile disposable component must interface with a plurality of sensors, integral with the fluid delivery system, to allow the accurate, reliable measurement of certain fluid physical properties. The measurements made by said sensors will allow the fluid delivery system to modify the physical properties of the biological fluid or otherwise effect certain operations of the fluid delivery system.